Gradual decoding refresh access unit in scalable video coding

ABSTRACT

Methods, devices and systems for configuring different access units in scalable video coding are described. In one example aspect, a method of video processing include performing a conversion between a video including one or more pictures in one or more video layers and a bitstream of a video. The bitstream includes a coded video sequence that includes one or more access units. The bitstream conforms to a format rule that specifies that each access unit of the one or more access units that is a gradual decoding refresh access unit includes exactly one picture for each video layer present in the coded video sequence.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/US2021/022404 filed on Mar. 15, 2021, which claims the priorityto and benefits of U.S. Provisional Pat. Application No. US 62/990,387filed on Mar. 16, 2020. All the aforementioned patent applications arehereby incorporated by reference in their entireties.

TECHNICAL FIELD

This patent document relates to image and video coding and decoding.

BACKGROUND

Digital video accounts for the largest bandwidth use on the internet andother digital communication networks. As the number of connected userdevices capable of receiving and displaying video increases, it isexpected that the bandwidth demand for digital video usage will continueto grow.

SUMMARY

The present document discloses techniques that include configuringdifferent access units in scalable video coding and that can be used byvideo encoders and decoders for processing coded representation of videousing control information useful for decoding of the codedrepresentation.

In one example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video comprising oneor more pictures in one or more video layers and a bitstream of a video,wherein the bitstream comprises a coded video sequence that includes oneor more access units, and wherein the bitstream further comprises afirst syntax element indicating whether an access unit includes apicture for each video layer making up the coded video sequence.

In another example aspect, a video processing method is disclosed. Themethod includes performing a conversion between a video comprising oneor more pictures in one or more video layers and a bitstream of thevideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that each picture in a given access unitcarries a layer identifier that is equal to a layer identifier of afirst access unit of the coded video sequence comprising the one or morevideo layers.

In yet another example aspect, a video processing method is disclosed.The method includes performing, a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of avideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream furthercomprises a first syntax element indicative of an access unit of the oneor more access units starting a new coded video sequence.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of thevideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that a coded video sequence start accessunit, which starts a new coded video sequence, comprises a picture foreach video layer specified in a video parameter set.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of thevideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that a given access unit is identified as acoded video sequence start access unit based on the given access unitbeing a first access unit in the bitstream or an access unit previous tothe given access unit comprising end of sequence network abstractionlayer units.

In yet another example aspect, a video processing method is disclosed.The method includes performing, based on a rule, a conversion between avideo comprising one or more pictures in one or more video layers and abitstream of the video, wherein the bitstream comprises a coded videosequence that includes one or more access units, and wherein the rulespecifies that side information is used to indicate whether an accessunit of the one or more access units is a coded video sequence startaccess unit.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of avideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that each access unit of the one or moreaccess units that is a gradual decoding refresh access unit includesexactly one picture for each video layer present in the coded videosequence.

In yet another example aspect, a video processing method is disclosed.The method includes performing a conversion between a video comprisingone or more pictures in one or more video layers and a bitstream of avideo, wherein the bitstream comprises a coded video sequence thatincludes one or more access units, and wherein the bitstream conforms toa format rule that specifies that each access unit of the one or moreaccess units that is an intra random access points access unit includesexactly one picture for each video layer present in the coded videosequence.

In yet another example aspect, a video encoder apparatus is disclosed.The video encoder comprises a processor configured to implementabove-described methods.

In yet another example aspect, a video decoder apparatus is disclosed.The video decoder comprises a processor configured to implementabove-described methods.

In yet another example aspect, a computer readable medium having codestored thereon is disclose. The code embodies one of the methodsdescribed herein in the form of processorexecutable code.

These, and other, features are described throughout the presentdocument.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an example video processing system inwhich various techniques disclosed herein may be implemented.

FIG. 2 is a block diagram of an example hardware platform used for videoprocessing.

FIG. 3 is a block diagram that illustrates an example video codingsystem that can implement some embodiments of the present disclosure.

FIG. 4 is a block diagram that illustrates an example of an encoder thatcan implement some embodiments of the present disclosure.

FIG. 5 is a block diagram that illustrates an example of a decoder thatcan implement some embodiments of the present disclosure.

FIGS. 6-13 show flowcharts for example methods of video processing.

DETAILED DESCRIPTION

Section headings are used in the present document for ease ofunderstanding and do not limit the applicability of techniques andembodiments disclosed in each section only to that section. Furthermore,H.266 terminology is used in some description only for ease ofunderstanding and not for limiting scope of the disclosed techniques. Assuch, the techniques described herein are applicable to other videocodec protocols and designs also.

1. Initial Discussion

This document is related to video coding technologies. Specifically, itis about specifying and signaling of random access point access unit inscalable video coding, wherein a video bitstream can contains more thanone layer. The ideas may be applied individually or in variouscombination, to any video coding standard or non-standard video codecthat supports multi-layer video coding, e.g., the being-developedVersatile Video Coding (VVC).

2. Abbreviations

-   APS Adaptation Parameter Set-   AU Access Unit-   AUD Access Unit Delimiter-   AVC Advanced Video Coding-   CLVS Coded Layer Video Sequence-   CPB Coded Picture Buffer-   CRA Clean Random Access-   CTU Coding Tree Unit-   CVS Coded Video Sequence-   DCI Decoding Capability Information-   DPB Decoded Picture Buffer-   EOB End Of Bitstream-   EOS End Of Sequence-   GDR Gradual Decoding Refresh-   HEVC High Efficiency Video Coding-   HRD Hypothetical Reference Decoder-   IDR Instantaneous Decoding Refresh-   JEM Joint Exploration Model-   MCTS Motion-Constrained Tile Sets-   NAL Network Abstraction Layer-   NUT NAL Unit Type-   OLS Output Layer Set-   PH Picture Header-   PPS Picture Parameter Set-   PTL Profile, Tier and Level-   PU Picture Unit-   RADL Random Access Decodable Leading-   RASL Random Access Skipped Leading-   RAP Random Access Point-   RBSP Raw Byte Sequence Payload-   SEI Supplemental Enhancement Information-   SPS Sequence Parameter Set-   SVC Scalable Video Coding-   VCL Video Coding Layer-   VPS Video Parameter Set-   VTM VVC Test Model-   VUI Video Usability Information-   VVC Versatile Video Coding

3. Video Coding Introduction

Video coding standards have evolved primarily through the development ofthe well-known International Telecommunication Union - TelecommunicationStandardization Sector (ITU-T) and International Organization forStandardization (ISO)/International Electrotechnical Commission (IEC)standards. The ITU-T produced H.261 and H.263, ISO/IEC produced MovingPicture Experts Group (MPEG)-1 and MPEG-4 Visual, and the twoorganizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, thevideo coding standards are based on the hybrid video coding structurewherein temporal prediction plus transform coding are utilized. Toexplore the future video coding technologies beyond HEVC, the JointVideo Exploration Team (JVET) was founded by Video Coding Experts Group(VCEG) and MPEG jointly in 2015. Since then, many new methods have beenadopted by JVET and put into the reference software named JointExploration Model (JEM). The JVET meeting is concurrently held onceevery quarter, and the new coding standard is targeting at 50% bitratereduction as compared to HEVC. The new video coding standard wasofficially named as Versatile Video Coding (VVC) in the April 2018 JVETmeeting, and the first version of VVC test model (VTM) was released atthat time. As there are continuous effort contributing to VVCstandardization, new coding techniques are being adopted to the VVCstandard in every JVET meeting. The VVC working draft and test model VTMare then updated after every meeting. The VVC project is now aiming fortechnical completion (FDIS) at the July 2020 meeting.

3.1. Random Access and Its Supports in HEVC and VVC

Random access refers to starting access and decoding of a bitstream froma picture that is not the first picture of the bitstream in decodingorder. To support tuning in and channel switching in broadcast/multicastand multiparty video conferencing, seeking in local playback andstreaming, as well as stream adaptation in streaming, the bitstreamneeds to include frequent random access points, which are typicallyintra coded pictures but may also be inter-coded pictures (e.g., in thecase of gradual decoding refresh).

HEVC includes signaling of intra random access points (IRAP) pictures inthe NAL unit header, through NAL unit types. Three types of IRAPpictures are supported, namely instantaneous decoder refresh (IDR),clean random access (CRA), and broken link access (BLA) pictures. IDRpictures are constraining the inter-picture prediction structure to notreference any picture before the current group-of-pictures (GOP),conventionally referred to as closed-GOP random access points. CRApictures are less restrictive by allowing certain pictures to referencepictures before the current GOP, all of which are discarded in case of arandom access. CRA pictures are conventionally referred to as open-GOPrandom access points. BLA pictures usually originate from splicing oftwo bitstreams or part thereof at a CRA picture, e.g., during streamswitching. To enable better systems usage of IRAP pictures, altogethersix different NAL units are defined to signal the properties of the IRAPpictures, which can be used to better match the stream access pointtypes as defined in the ISO base media file format (ISOBMFF), which areutilized for random access support in dynamic adaptive streaming overHTTP (DASH).

VVC supports three types of IRAP pictures, two types of IDR pictures(one type with or the other type without associated RADL pictures) andone type of CRA picture. These are basically the same as in HEVC. TheBLA picture types in HEVC are not included in VVC, mainly due to tworeasons: i) The basic functionality of BLA pictures can be realized byCRA pictures plus the end of sequence NAL unit, the presence of whichindicates that the subsequent picture starts a new CVS in a single-layerbitstream. ii) There was a desire in specifying less NAL unit types thanHEVC during the development of VVC, as indicated by the use of fiveinstead of six bits for the NAL unit type field in the NAL unit header.

Another key difference in random access support between VVC and HEVC isthe support of GDR in a more normative manner in VVC. In GDR, thedecoding of a bitstream can start from an inter-coded picture andalthough at the beginning not the entire picture region can be correctlydecoded but after a number of pictures the entire picture region wouldbe correct. AVC and HEVC also support GDR, using the recovery point SEImessage for signaling of GDR random access points and the recoverypoints. In VVC, a new NAL unit type is specified for indication of GDRpictures and the recovery point is signaled in the picture header syntaxstructure. A CVS and a bitstream are allowed to start with a GDRpicture. This means that it is allowed for an entire bitstream tocontain only inter-coded pictures without a single intra-coded picture.The main benefit of specifying GDR support this way is to provide aconforming behavior for GDR. GDR enables encoders to smooth the bit rateof a bitstream by distributing intra-coded slices or blocks in multiplepictures as opposed intra coding entire pictures, thus allowingsignificant end-to-end delay reduction, which is considered moreimportant nowadays than before as ultralow delay applications likewireless display, online gaming, drone based applications become morepopular.

Another GDR related feature in VVC is the virtual boundary signaling.The boundary between the refreshed region (i.e., the correctly decodedregion) and the unrefreshed region at a picture between a GDR pictureand its recovery point can be signaled as a virtual boundary, and whensignaled, in-loop filtering across the boundary would not be applied,thus a decoding mismatch for some samples at or near the boundary wouldnot occur. This can be useful when the application determines to displaythe correctly decoded regions during the GDR process.

IRAP pictures and GDR pictures can be collectively referred to as randomaccess point (RAP) pictures.

3.2. Scalable Video Coding (SVC) in General and in VVC

Scalable video coding (SVC, sometimes also just referred to asscalability in video coding) refers to video coding in which a baselayer (BL), sometimes referred to as a reference layer (RL), and one ormore scalable enhancement layers (ELs) are used. In SVC, the base layercan carry video data with a base level of quality. The one or moreenhancement layers can carry additional video data to support, forexample, higher spatial, temporal, and/or signal-to-noise (SNR) levels.Enhancement layers may be defined relative to a previously encodedlayer. For example, a bottom layer may serve as a BL, while a top layermay serve as an EL. Middle layers may serve as either ELs or RLs, orboth. For example, a middle layer (e.g., a layer that is neither thelowest layer nor the highest layer) may be an EL for the layers belowthe middle layer, such as the base layer or any intervening enhancementlayers, and at the same time serve as a RL for one or more enhancementlayers above the middle layer. Similarly, in the Multiview or threedimensional (3D) extension of the HEVC standard, there may be multipleviews, and information of one view may be utilized to code (e.g., encodeor decode) the information of another view (e.g., motion estimation,motion vector prediction and/or other redundancies).

In SVC, the parameters used by the encoder or the decoder are groupedinto parameter sets based on the coding level (e.g., video-level,sequence-level, picture-level, slice level, etc.) in which they may beutilized. For example, parameters that may be utilized by one or morecoded video sequences of different layers in the bitstream may beincluded in a video parameter set (VPS), and parameters that areutilized by one or more pictures in a coded video sequence may beincluded in a sequence parameter set (SPS). Similarly, parameters thatare utilized by one or more slices in a picture may be included in apicture parameter set (PPS), and other parameters that are specific to asingle slice may be included in a slice header. Similarly, theindication of which parameter set(s) a particular layer is using at agiven time may be provided at various coding levels.

Thanks to the support of reference picture resampling (RPR) in VVC,support of a bitstream containing multiple layers, e.g., two layers withstandard definition (SD) and high definition (HD) resolutions in VVC canbe designed without the need any additional signalprocessing-levelcoding tool, as upsampling needed for spatial scalability support canjust use the RPR upsampling filter. Nevertheless, high-level syntaxchanges (compared to not supporting scalability) are needed forscalability support. Scalability support is specified in VVC version 1.Different from the scalability supports in any earlier video codingstandards, including in extensions of AVC and HEVC, the design of VVCscalability has been made friendly to single-layer decoder designs asmuch as possible. The decoding capability for multi-layer bitstreams arespecified in a manner as if there were only a single layer in thebitstream. E.g., the decoding capability, such as DPB size, is specifiedin a manner that is independent of the number of layers in the bitstreamto be decoded. Basically, a decoder designed for single-layer bitstreamsdoes not need much change to be able to decode multi-layer bitstreams.Compared to the designs of multi-layer extensions of AVC and HEVC, thehigh-level syntax (HLS) aspects have been significantly simplified atthe sacrifice of some flexibilities. For example, an IRAP AU is requiredto contain a picture for each of the layers present in the CVS.

3.3. Parameter Sets

AVC, HEVC, and VVC specify parameter sets. The types of parameter setsinclude SPS, PPS, APS, and VPS. SPS and PPS are supported in all of AVC,HEVC, and VVC. VPS was introduced since HEVC and is included in bothHEVC and VVC. APS was not included in AVC or HEVC but is included in thelatest VVC draft text.

SPS was designed to carry sequence-level header information, and PPS wasdesigned to carry infrequently changing picture-level headerinformation. With SPS and PPS, infrequently changing information neednot to be repeated for each sequence or picture, hence redundantsignaled of this information can be avoided. Furthermore, the use of SPSand PPS enables out-ofband transmission of the important headerinformation, thus not only avoiding the need for redundant transmissionsbut also improving error resilience.

VPS was introduced for carrying sequence-level header information thatis common for all layers in multi-layer bitstreams.

APS was introduced for carrying such picture-level or slice-levelinformation that needs quite some bits to code, can be shared bymultiple pictures, and in a sequence there can be quite many differentvariations.

3.4. Related Definitions in in VVC

Related definitions in the latest VVC text (in JVET-Q2001-Ve/v15) are asfollows.

-   Associated IRAP picture (of a particular picture): The previous IRAP    picture in decoding order (when present) having the same value of    nuh_layer_id as the particular picture.-   Coded video sequence (CVS): A sequence of AUs that consists, in    decoding order, of a CVSS AU, followed by zero or more AUs that are    not CVSS AUs, including all subsequent AUs up to but not including    any subsequent AU that is a CVSS AU. Coded video sequence start    (CVSS) AU: An AU in which there is a PU for each layer in the CVS    and the coded picture in each PU is a CLVSS picture.-   Gradual decoding refresh (GDR) AU: An AU in which the coded picture    in each present PU is a GDR picture.-   Gradual decoding refresh (GDR) PU: A PU in which the coded picture    is a GDR picture.-   Gradual decoding refresh (GDR) picture: A picture for which each VCL    NAL unit has nal_unit_type equal to GDR_NUT.-   Intra random access point (IRAP) AU: An AU in which there is a PU    for each layer in the CVS and the coded picture in each PU is an    IRAP picture.-   Intra random access point (IRAP) picture: A coded picture for which    all VCL NAL units have the same value of nal_unit_type in the range    of IDR_W_RADL to CRA_NUT, inclusive.

3.5. VPS Syntax and Semantics in VVC

VVC supports scalability, also known as scalable video coding, whereinmultiple layers can be encoded in one coded video bitstream.

In the latest VVC text (in JVET-Q2001-Ve/v15), the scalabilityinformation is signaled in the VPS, for which the syntax and semanticsare as follows. 7.3.2.2 Video parameter set syntax

video_parameter_set rbsp() { Descriptor vps_video_parameter_set_id u(4)vps_max_layers_minus1 u(6) vps_max_sublayers_minus1 u(3) if(vps_max_layers_minus1 > 0 && vps _max_sublayers_minus 1 > 0 )vps_all_layers_same_num_sublayers_flag u(1) if( vps_max_layers_minus1 >0 ) vps_all_independent_layers_flag u(1) for( I = 0; I <=vps_max_layers_minus1; i++ ) { vps_layer_id[ I ] u(6) if( I > 0 &&!vps_all_independent_layers_flag ) { vps_independent_layer_flag[ I ]u(1) if( !vps_independent_layer_flag[ I ] ) { for( j = 0; j < I; j++ )vps_direct_ref_layer_flag[ I ] [j] u(1) max_tid_ref_present_flag[ I ]u(1) if( max_tid_ref_present_flag[ I ] ) max_tid_il_ref_pics_plus1 [ I ]u(3) } } } if( vps_max_layers_minus1 > 0 ) { if(vps_all_independent_layers _flag) each_layer_is_an_ols_flag u(1) if(!each_layer_is_an_ols_flag) { if( !vps_all_independent_layers_flag)ols_mode_idc u(2) if( ols_mode_idc = = 2) { num_output_layer_sets_minus1u(8) for( I = 1; I <= num_output_layer_sets_minus 1; I ++) for(j = 0; j<= vps_max_layers_minus1; j++ ) ols_output_layer_flag[ I ][ j ] u(1) } }} vps_num_ptls_minus1 u(8) for( I = 0; I <= vps_num_ptls_minus1; i++ ) {if (I>0) pt_present_flag[ I ] u(1) if( vps_max_sublayers_minus 1 > 0 &&!vps_all _layers_same_num_sublayers_flag) ptt_max_temporal_id[ I ] u(3)} } while(!byte_aligned( ) ) vps_ptl_alignment_zero_bit /* equal to 0 */f(1) for( I = 0; I <= vps_num_ptls_minus1; i++ )profile_tier_level(pt_present_flag[I], ptl_max_temporal_id[ I ]) for( I= 0; I < TotalNumOlss; i++ ) if(vps_num_ptls_minus1 > 0) ols_ptl_idx[I]u(8) if(!vps_all_independent_layers_flag) vps_num_dpb_params ue(v)if(vps_num_dpb_params > 0 && vps_max_sublayers_minus1 > 0)vps_sublayer_dpb_params_present_flag u(1) for( I = 0; I <vps_num_dpb_params; i++) { if(vps_max_sublayers_minus1 > 0 && !vps_all_layers_same_num_sublayers_flag) dpb_max_temporal_id[I] u(3)dpb_parameters(dpb_max_temporal_id[I],vps_sublayer_dpb_params_present_flag) } for( I = 0; I < TotalNumOlss;i++ ) { if(NumLayersInOls[I] > 1) { ols_dpb_pic_width[I] ue(v)ols_dpb_pic_height[I] ue(v) if( vps_num_dpb_params > 1)ols_dpb_params_idx[I] ue(v) } } if(!each_layer_is_an_ols_flag)vps_general_hrd_params_present_flag u(1) if(vps_general_hrd_params_present_flag) { general _hrd_parameters()if(vps_max_sublayers_minus1 > 0) vps_sublayer_cpb_params_present_flagu(1) num_ols_hrd_params_minus1 ue(v) for( I = 0; I <=num_ols_hrd_params_minus1; i++) { if(vps _max__sublayers_minus1 > 0 &&!vps_all _layers_same_num_sublayers_flag) hrd_max_tid[I] u(3)firstSubLayer = vps_sublayer_cpb_params_present_flag ? 0 :hrd_max_tid[I]ols_hrd_parameters(firstSubLayer, hrd__max_tid[I]) } if(num_ols_hrd_paramsminus1 + 1!= TotalNumOlss &&num_ols_hrd_params_minus1> 0 ) for( I = 1; I < TotalNumOlss; i++ )if(NumLayersInO1s[I] > 1) ols_hrd_idx[I] ue(v) } vps_extension_flag u(1)if( vps_extension_flag ) while( more_rbsp_data() ) vps_extension_data_flag u(1) rbsp_trailing_bits() }

7.4.3.2 Video Parameter Set RBSP Semantics

A VPS RBSP shall be available to the decoding process prior to it beingreferenced, included in at least one AU with TemporalId equal to 0 orprovided through external means.

All VPS NAL units with a particular value of vps_video_parameter_set_idin a CVS shall have the same content.

Vps_video_parameter_set_id provides an identifier for the VPS forreference by other syntax elements. The value of vps_video_parameter_set_id shall be greater than 0.

Vps_max_layers_minus1 plus 1specifies the maximum allowed number oflayers in each CVS referring to the VPS.

Vps_max_sublayers_minus1 plus 1specifies the maximum number of temporalsublayers that may be present in a layer in each CVS referring to theVPS. The value of vps_max_sublayers_minus1 shall be in the range of 0 to6, inclusive.

Vps_all_layers_same_num_sublayers_flag equal to 1specifies that thenumber of temporal sublayers is the same for all the layers in each CVSreferring to the VPS. Vps_all_layers_same_num_sublayers_flag equal to 0specifies that the layers in each CVS referring to the VPS may or maynot have the same number of temporal sublayers. When not present, thevalue of vps_all_layers_same_num_sublayers_flag is inferred to be equalto 1.

Vps_all independent layers flag equal to 1specifies that all layers inthe CVS are independently coded without using inter-layer prediction.Vps_all _independent_layers_flag equal to 0 specifies that one or moreof the layers in the CVS may use inter-layer prediction. When notpresent, the value of vps_all_independent_layers _flag is inferred to beequal to 1.

Vps_layer_id[I] specifies the nuh_layer_id value of the i-th layer. Forany two non-negative integer values of m and n, when m is less than n,the value of vps_layer_id[m] shall be less than vps_layer_id[n].

Vps_independent_layer_flag[I] ┊ equal to 1specifies that the layer withindex I does not use inter-layer prediction. Vps_independent_layer_flag[I] equal to 0 specifies that the layer with index I may useinter-layer prediction and the syntax elementsvps_direct_ref_layer_flag[I][j] for j in the range of 0 to I - 1,inclusive, are present in VPS. When not present, the value ofvps_independent_layer_flag[I] ┊ is inferred to be equal to 1.

Vps_direct_ref_layer_flag[I][j] equal to 0 specifies that the layer withindex j is not a direct reference layer for the layer with index i.vps_direct__ref_ layer _flag [I][j] equal to 1specifies that the layerwith index j is a direct reference layer for the layer with index i.When vps_direct__ref_layer_flag[I][j] is not present for I and j in therange of 0 to vps_max_layers_minus1, inclusive, it is inferred to beequal to 0. When vps_independent_layer_flag[I] ┊ is equal to 0, thereshall be at least one value of j in the range of 0 to I - 1, inclusive,such that the value of vps_direct_ref_layer_flag[I] [j] is equal to 1.

The variables NumDirectRefLayers[I], DirectRefLayerIdx[I][d],NumRefLayers[I], RefLayerIdx[I][r], and LayerUsedAsRefLayerFlag[j] arederived as follows:

for( I = 0; I <= vps_max_layers_minus1; i++) {           for(j = 0; j <= vps_max_layers_minus1; j++) {               dependencyFlag[I][j] = vps_direct_ref_layer_flag[I][j]               for( k = 0; k < I; k++)                        if( vps_direct_ref_layer_flag[I][k] && dependencyFlag[k][j])       }}dependencyFlag[I][j] = 1           LayerUsedAsRefLayerFlag[I] = 0       for( I = 0; I <= vps_max_layers_minus1; i++){           for(j = 0, d = 0, r = 0; j <= vps__max_layersminus1; j++){ (37)               if( vps_direct_ref_layer_flag[I][j] ) {                        DirectRefLayerIdx[I][d++] = j                        LayerUsedAsRefLayerFlag[j] = 1               if( dependencyFlag[I][j])           }}RefLayerIdx[I ][r++] = j           NumDirectRefLayers[I] ┊ = d        }NumRefLayers[I] = r

The variable GeneralLayerIdx[I], specifying the layer index of the layerwith nuh_layer_id equal to vps _layer_id[I], is derived as follows:

for( I = 0; I <= vps_max_layers_minus1; i++) (38)           GeneralLayerIdx[vps _layer_id[I ] ] = i

For any two different values of I and j, both in the range of 0 tovps_max_layers_minus1, inclusive, when dependencyFlag[I ][j] equal to 1,it is a requirement of bitstream conformance that the values ofchroma_format_idc and bit_depth_minus8 that apply to the i-th layershall be equal to the values of chroma_format_idc and bit_depth _minus8,respectively, that apply to the j-th layer.

Max_tid_ref_present_flag[I] ┊ equal to 1specifies that the syntaxelement max_tid_il_ref_pics_plus1[I] is present.Max_tid_ref_present_flag[I] ┊ equal to 0 specifies that the syntaxelement max_tid_il_ref_pics_plus1[I] is not present.

Max_tid_il_ref_pics_plus1[I] equal to 0 specifies that inter-layerprediction is not used by non-IRAP pictures of the i-th layer.Max_tid_il_ref_pics_plus[I] greater than 0 specifies that, for decodingpictures of the i-th layer, no picture with TemporalId greater thanmax_tid_il_ref_pics_plus1[I] ┊ - 1is used as ILRP. When not present, thevalue of _max_tid_il_ref_pics_plus1[I] ┊ is inferred to be equal to 7.

Each_layer_is_an_ols_flag equal to 1 specifies that each OLS containsonly one layer and each layer itself in a CVS referring to the VPS is anOLS with the single included layer being the only output layer.Each_layer_is_an_ols_flag equal to 0 that an OLS may contain more thanone layer. If vps _max_layers_minus1is equal to 0, the value ofeach_layer_is_an_ols _flag is inferred to be equal to 1. Otherwise, whenvps_all_independent_layers_flag is equal to 0, the value ofeach_layer_is_an_ols_flag is inferred to be equal to 0.

Ols_mode_idc equal to 0 specifies that the total number of OLSsspecified by the VPS is equal to vps_max_layers_minus1 + 1, the i-th OLSincludes the layers with layer indices from 0 to I, inclusive, and foreach OLS only the highest layer in the OLS is output.

Ols_mode_idc equal to 1 specifies that the total number of OLSsspecified by the VPS is equal to vps_max_layers_minus1 + 1, the i-th OLSincludes the layers with layer indices from 0 to I, inclusive, and foreach OLS all layers in the OLS are output.

Ols_mode_idc equal to 2 specifies that the total number of OLSsspecified by the VPS is explicitly signalled and for each OLS the outputlayers are explicitly signalled and other layers are the layers that aredirect or indirect reference layers of the output layers of the OLS.

The value of ols_mode_idc shall be in the range of 0 to 2, inclusive.The value 3 of ols _mode_idc is reserved for future use by ITU-T |ISO/IEC.

When vps_all_independent_layers_flag is equal to 1 andeach_layer_is_an_ols_flag is equal to 0, the value of ols _mode_idc isinferred to be equal to 2.

Num_output_layer_sets_minus1 plus 1 specifies the total number of OLSsspecified by the VPS when ols_mode_idc is equal to 2.

The variable TotalNumOlss, specifying the total number of OLSs specifiedby the VPS, is derived as follows:

if( vps _max_layers_minus1= = 0)            TotalNumOlss = 1       else if( each_layer_is_an_ols_flag || ols_mode_idc = = 0 || ols_mode_idc = = 1)           TotalNumOlss = vps_max_layers_minus1 + 1 (39)       else if(ols_mode_idc = = 2 )           TotalNumOlss = num_output_layer_sets_minus1 + 1

ols_output_layer_flag[I][j] equal to 1 specifies that the layer withnuh_layer_id equal to vps_layer_id[j] is an output layer of the i-th OLSwhen ols_mode_idc is equal to 2. Ols_output_layer_flag[I][j] equal to 0specifies that the layer with nuh_layer_id equal to vps_layer_id[j] isnot an output layer of the i-th OLS when ols_mode_idc is equal to 2.

The variable NumOutputLayersInOls[I], specifying the number of outputlayers in the i-th OLS, the variable NumSubLayersInLayerInOLS[I][j],specifying the number of sublayers in the j-th layer in the i-th OLS,the variable OutputLayerIdInOls[I][j], specifying the nuh_layer_id valueof the j-th output layer in the i-th OLS, and the variableLayerUsedAsOutputLayerFlag[k], specifying whether the k-th layer is usedas an output layer in at least one OLS, are derived as follows:

NumOutputLayersInOls[0] = 1       OutputLayerIdInOls[0][0] = vps_layer_id[0]       NumSubLayersInLayerInOLS[0][0] = vps_max_sub_layers_minus1 + 1       LayerUsedAsOutputLayerFlag[0] = 1       for( I = 1, I <= vps_max_layers_minus1; i++) {           if( each_layer_is_an_ols_flag || ols_mode_idc < 2)               LayerUsedAsOutputLayerFlag[I] = 1           else /*(!each_layer_is_an_ols_flag && ols_mode_idc == 2 ) */       }LayerUsedAsOutputLayerFlag[I] = 0       for( I = 1; I < TotalNumOlss; i++ )           if( each_layer_is_an_ols_flag || ols_mode_idc = = 0) {               NumOutputLayersInOls[I] = 1               OutputLayerIdInOls[I ][0] = vps _layer_id[I]               for(j= 0; j< I && (ols_mode_idc = = 0); j++)                        NumSubLayersInLayerInOLS[I][j] = max_tid_il_ref_pics_plus1[I]               NumSubLayersInLayerInOLS[I] [I] ┊ = vps_max_sub_layers_minus1 + 1           } else if( ols_mode_idc = = 1) {               NumOutputLayersInOls[I] = I + 1               for(j = 0; j < NumOutputLayersInOls[I]; j++) {                        OutputLayerIdInOls[I][j] = vps_layer_id[j]               }NumSubLayersInLayerInOLS[I][j] = vps_max_sub_layers_minus1 + 1           } else if( ols_mode_idc = = 2 ) {               for(j = 0; j <= vps_max_layers_minus1; j++) {                        layerIncludedInOlsFlag[I][j] = 0               }NumSubLayersInLayerInOLS[I][j] = 0               for( k = 0, j = 0; k <= vps _max_layers_minus1; k++) (40)                        if(ols_output_layer_flag[I][k]) {                                 layerIncludedInOlsFlag[I][k] = 1                                 LayerUsedAsOutputLayerFlag[k] = 1                                 OutputLayerIdx[I][j] = k                                 OutputLayerIdInOls[I][j++] = vps _layer_id[k]                                 NumSubLayersInLayerInOLS[I][j] =       vps_max_sub_layers_minus1 + 1                         }               NumOutputLayersInOls[I] = j               for(j = 0; j < NumOutputLayersInOls[I]; j++) {                        idx = OutputLayerIdx[I] [j]                        for( k = 0; k < NumRefLayers[idx]; k++) {                                 layerIncludedInOlsFlag[I][RefLayerIdx[idx][k] ] = 1                                 if( NumSubLayersInLayerInOLS[I][RefLayerIdx[idx][k]] <           max_tid_il_ref_pics_plus1[OutputLayerIdInOls [I][j] ])                                         NumSubLayersInLayerInOLS[I][RefLayerIdx[idx][k]] =           max_tid_il_ref_pics_plus1[OutputLayerIdInOls[I][j] ]           }}}

For each value of I in the range of 0 to vps_max_layers_minus1,inclusive, the values of LayerUsedAsRefLayerFlag[I] ┊ andLayerUsedAsOutputLayerFlag[I] ┊ shall not be both equal to 0. In otherwords, there shall be no layer that is neither an output layer of atleast one OLS nor a direct reference layer of any other layer.

For each OLS, there shall be at least one layer that is an output layer.In other words, for any value of I in the range of 0 to TotalNumOlss -1, inclusive, the value of NumOutputLayersInOls[I] ┊ shall be greaterthan or equal to 1.

The variable NumLayersInOls[I], specifying the number of layers in thei-th OLS, and the variable LayerIdInOls[I][j], specifying thenuh_layer_id value of the j-th layer in the i-th OLS, are derived asfollows:

NumLayersInOls[0] = 1        LayerIdInOls[0][0] = vps _layer_id[0]       for( I = 1; I < TotalNumOlss; i++ ) {           if(each_layer_is_an_ols_flag){               NumLayersInOls[I] = 1               LayerIdInOls[I][0] = vps_layer_id[I] ┊ (41)           } else if( ols_mode_idc = = 0 || ols_mode_idc = = 1){               NumLayersInOls[I] = I + 1               for(j= 0; j < NumLayersInOls[I]; j++)                        LayerIdInOls[I][j] = vps _layer_id[j]           } else if( ols_mode_idc = = 2){               for( k = 0, j = 0; k <= vps _max_layers_minus1; k++)                        if(layerIncludedInOlsFlag[I][k])                                 LayerIdInOls[ I ][ j++ ] = vps _layer_id[ k ]       }}NumLayersInOls[I ] = j

NOTE 1-The 0-th OLS contains only the lowest layer (i.e., the layer withnuh _layer_id equal to vps layer_id[ 0 ]) and for the 0-th OLS the onlyincluded layer is output.

The variable OlsLayerIdx[ I ][j ], specifying the OLS layer index of thelayer with nuh_layer_id equal to LayerIdInOls[ I ][ j ], is derived asfollows:

       for( I = 0; I < TotalNumOlss; i++ )           for j = 0; j < NumLayersInOls[I ]; j++ ) (42)               OlsLayerIdx[ I ][ LayerIdInOls [ I ] [ j ] ] = j

The lowest layer in each OLS shall be an independent layer. In otherwords, for each I in the range of 0 to TotalNumOlss - 1, inclusive, thevalue of

vps _independent _layer__flag[ GeneralLayerIdx[ LayerIdInOls[ I ][ 0 ] ]] shall be equal to 1.

Each layer shall be included in at least one OLS specified by the VPS.In other words, for each layer with a particular value of nuh_layer_idnuhLayerId equal to one of vps_layer_id[ k ] for k in the range of 0 tovps_max_layers_minus1, inclusive, there shall be at least one pair ofvalues of I and j, where I is in the range of 0 to TotalNumOlss - 1,inclusive, and j is in the range of NumLayersInOls[ I ] - 1, inclusive,such that the value of LayerIdInOls [ I ] [ j ] is equal to nuhLayerId.

Vps_num_ptls_minus1 plus 1 specifies the number of profile_tier_level()syntax structures in the VPS. The value of vps_num_ptls_minus1 shall beless than TotalNumOlss.

Pt_present_flag[ I ] equal to 1 specifies that profile, tier, andgeneral constraints information are present in the i-thprofile_tier_level() syntax structure in the VPS. Pt_present_flag[ I ]equal to 0 specifies that profile, tier, and general constraintsinformation are not present in the i-th profile_tier_level() syntaxstructure in the VPS. The value of pt_present_flag[ 0 ] is inferred tobe equal to 1. When pt_present_flag[ I ] is equal to 0, the profile,tier, and general constraints information for the i-th profile_tier_level( ) syntax structure in the VPS are inferred to be the same asthat for the ( I - 1 )-th profile_tier_level() syntax structure in theVPS.

Ptl_max_temporal_id[ I ] specifies the TemporalId of the highestsublayer representation for which the level information is present inthe i-th profile_tier_level() syntax structure in the VPS. The value ofptl_max_temporal_id[ I ] shall be in the range of 0 tovps_max_sublayers_minus1, inclusive. When vps_max_sublayers_minus1 isequal to 0, the value of ptl_max_temporal_id[ I ] is inferred to beequal to 0. When vps_max_sublayers_minus1 is greater than 0 andvps_all_layers_same_num_sublayers_flag is equal to 1, the value ofptl_max_temporal_id[ I ] is inferred to be equal tovps_max_sublayers_minus1. Vps_ptl_alignment_zero_bit shall be equal to0.

Ols_ptl_idx[ I ] specifies the index, to the list ofprofile_tier_level() syntax structures in the VPS, of theprofile_tier_level() syntax structure that applies to the i-th OLS. Whenpresent, the value of ols_ptl_idx[ I ] shall be in the range of 0 tovps­_num_ptls_minus1, inclusive. When vps_num_ptls_minus1 is equal to 0,the value of ols_ptl_idx[ I ] is inferred to be equal to 0.

When NumLayersInOls[I ] is equal to 1, the profile_tier_level() syntaxstructure that applies to the i-th OLS is also present in the SPSreferred to by the layer in the i-th OLS. It is a requirement ofbitstream conformance that, when NumLayersInOls[I ] is equal to 1, theprofile_tier_level() syntax structures signalled in the VPS and in theSPS for the i-th OLS shall be identical.

Vps_num_dpb_params specifies the number of dpb_parameters( ) syntaxstructures in the VPS. The value of vps_num_dpb_params shall be in therange of 0 to 16, inclusive. When not present, the value of vpsnum_dpb_params is inferred to be equal to 0.

Vps_sublayer_dpb_params_present_flag is used to control the presence ofmax_dec_pic_buffering_minus1[ ], max_num_reorder_pics[ ], andmax_latency_increase_plus 1 [ ] syntax elements in the dpb_parameters()syntax structures in the VPS. When not present,vps_sub_dpb_params_info_present_flag is inferred to be equal to 0.

Dpb_max_temporal_id[ I ] specifies the TemporalId of the highestsublayer representation for which the DPB parameters may be present inthe i-th dpb_parameters() syntax structure in the VPS. The value ofdpb_max_temporal_id[ I ] shall be in the range of 0 tovps_max_sublayers_minus1, inclusive. When vps_max_sublayers_minus1 isequal to 0, the value of dpb_max_temporal_id[ I ] is inferred to beequal to 0. When vps_max_sublayers_minus1 is greater than 0 andvps_all_layers_same_num_sublayers_flag is equal to 1, the value ofdpb_max_temporal _id[ I ] is inferred to be equal tovps_max_sublayers_minus1.

Ols_dpb_pic- width[ I ] specifies the width, in units of luma samples,of each picture storage buffer for the i-th OLS.

Ols_dpb_pic_height[ I ] specifies the height, in units of luma samples,of each picture storage buffer for the i-th OLS.

Ols_dpb_params_idx[ I ] specifies the index, to the list ofdpb_parameters( ) syntax structures in the VPS, of the dpb_parameters()syntax structure that applies to the i-th OLS when NumLayersInOls[I ] isgreater than 1. When present, the value of ols_dpb_params_idx[ I ] shallbe in the range of 0 to vps_num_dpb_params - 1, inclusive. Whenols_dpb_params_idx[ I ] is not present, the value of ols_dpb_params_idx[I ] is inferred to be equal to 0.

When NumLayersInOls[I] is equal to 1, the dpb_parameters( ) syntaxstructure that applies to the i-th OLS is present in the SPS referred toby the layer in the i-th OLS.

Vps_general_hrd_params_present_flag equal to 1 specifies that the VPScontains a general_hrd_parameters( ) syntax structure and other HRDparameters.

Vps_general_hrd_params_present_flag equal to 0 specifies that the VPSdoes not contain a general _hrd_parameters( ) syntax structure or otherHRD parameters. When not present, the value ofvps_general_hrd_params_present_flag is inferred to be equal to 0.

When NumLayersInOls[I] is equal to 1, the general_hrd_parameters()syntax structure and the ols _hrd_parameters( ) syntax structure thatapply to the i-th OLS are present in the SPS referred to by the layer inthe i-th OLS.

Vps_sublayer_cpb_params_present_flag equal to 1 specifies that the i-thols_hrd_parameters() syntax structure in the VPS contains HRD parametersfor the sublayer representations with TemporalId in the range of 0 tohrd_max_tid[ I ], inclusive. Vps_sublayer_cpb_params_present _flag equalto 0 specifies that the i-th ols _hrd_parameters( ) syntax structure inthe VPS contains HRD parameters for the sublayer representation withTemporalId equal to hrd_max_tid[ I ] only. When vps_max_sublayers_minus1is equal to 0, the value of vps_sublayer_cpb_params_present_flag isinferred to be equal to 0.

When vps_sublayer_cpb_params_present_flag is equal to 0, the HRDparameters for the sublayer representations with TemporalId in the rangeof 0 to hrd_max_tid[ I ] - 1, inclusive, are inferred to be the same asthat for the sublayer representation with TemporalId equal tohrd_max_tid[ I ]. These include the HRD parameters starting from thefixed_pic_rate_general_flag[ I ] syntax element till the sublayer_hrd_parameters( I ) syntax structure immediately under the condition“if( general _vcl_hrd_params_present_flag )” in the ols_hrd_parameterssyntax structure. Num_ols_hrd_params_minus1 plus 1 specifies the numberof ols_hrd_parameters( ) syntax structures present in the VPS whenvps_general_hrd_params_present_flag is equal to 1. The value ofnum_ols_hrd_params_minus1 shall be in the range of 0 to TotalNumOlss -1, inclusive.

Hrd_max_tid[ I ] specifies the TemporalId of the highest sublayerrepresentation for which the HRD parameters are contained in the i-thols _hrd_parameters( ) syntax structure. The value of hrd_max_tid[ I ]shall be in the range of 0 to vps_max_sublayers_minus1, inclusive. Whenvps_max_sublayers_minus1 is equal to 0, the value of hrd_max_tid[ I ] isinferred to be equal to 0. When vps_max_sublayers_minus1 is greater than0 and vps_all_layers_same_num_sublayers_flag is equal to 1, the value ofhrd_max_tid[ I ] is inferred to be equal to vps_max_sublayers_minus1.

Ols_hrd_idx[ I ] specifies the index, to the list of ols_hrd_parameters() syntax structures in the VPS, of the ols_hrd_parameters() syntaxstructure that applies to the i-th OLS when NumLayersInOls[I] is greaterthan 1. The value of ols_hrd_idx[[ I ] shall be in the range of 0 tonum_ols_hrd_params_minus1, inclusive.

When NumLayersInOls[I] is equal to 1, the ols_hrd_parameters() syntaxstructure that applies to the i-th OLS is present in the SPS referred toby the layer in the i-th OLS.

If the value of num_ols_hrd_param_minus1 + 1 is equal to TotalNumOlss,the value of ols_hrd_idx[ I ] is inferred to be equal to i. Otherwise,when NumLayersInOls[I] is greater than 1 and num_ols_hrd_params_minus1is equal to 0, the value of ols_hrd_idx[[ I ] is inferred to be equal to0.

Vps_extension_flag equal to 0 specifies that no vps_extension_data_flagsyntax elements are present in the VPS RBSP syntax structure.Vps_extension_flag equal to 1 specifies that there arevps_extension_data _flag syntax elements present in the VPS RBSP syntaxstructure.

Vps_extension_data_flag may have any value. Its presence and value donot affect decoder conformance to profiles specified in this version ofthis Specification. Decoders conforming to this version of thisSpecification shall ignore all vps_extension_data _flag syntax elements.

3.6. Access Unit Delimiter (AUD) Syntax and Semantics in VVC

In the latest VVC text (in JVET-Q2001-Ve/v15), the AUD syntax andsemantics are as follows.

7.3.2.9 AU delimiter RBSP syntax access_unit_delimiter_rbsp( ) {Descriptor      pic_type u(3)      rbsp_trailing_bits() }

7.4.3.9 AU Delimiter RBSP Semantics

The AU delimiter is used to indicate the start of an AU and the type ofslices present in the coded pictures in the AU containing the AUdelimiter NAL unit. There is no normative decoding process associatedwith the AU delimiter.

Pic_type indicates that the slice_type values for all slices of thecoded pictures in the AU containing the AU delimiter NAL unit aremembers of the set listed in Table 7 for the given value of pic_type.The value of pic_type shall be equal to 0, 1 or 2 in bitstreamsconforming to this version of this Specification. Other values ofpic_type are reserved for future use by ITU-T ISO/IEC. Decodersconforming to this version of this Specification shall ignore reservedvalues of pic_type.

Table 7 Interpretation of pic_type pic_type slice_type values that maybe present in the AU 0 I 1 P, I 2 B, P, I

3.7. Order of AUs and PUs

In the latest VVC text (in JVET-Q2001-Ve/v15), the specification of thedecoding order of AUs and PUs is as follows.

7.4.2.4.2 Order of AUs and Their Association to CVSs

A bitstream consists of one or more CVSs.

A CVS consists of one or more AUs. The order of PUs and theirassociation to AUs are described in clause 7.4.2.4.3.

The first AU of a CVS is a CVSS AU, wherein each present PU is a CLVSSPU, which is either an IRAP PU with NoOutputBeforeRecoveryFlag equal to1 or a GDR PU with NoOutputBeforeRecoveryFlag equal to 1.

Each CVSS AU shall have a PU for each of the layers present in the CVS.

7.4.2.4.3 Order of PUs and Their Association to AUs

An AU consists of one or more PUs in increasing order of nuh _layer_id.The order NAL units and coded pictures and their association to PUs aredescribed in clause 7.4.2.4.4.

There can be at most one AUD NAL unit in an AU. When an AUD NAL unit ispresent in an AU, it shall be the first NAL unit of the AU, andconsequently, it is the first NAL unit of the first PU of the AU.

There can be at most one EOB NAL unit in an AU. When an EOB NAL unit ispresent in an AU, it shall be the last NAL unit of the AU, andconsequently, it is the last NAL unit of the last PU of the AU.

A VCL NAL unit is the first VCL NAL unit of an AU (and consequently thePU containing the VCL NAL unit is the first PU of the AU) when the VCLNAL unit is the first VCL NAL unit that follows a PH NAL unit and one ormore of the following conditions are true:

-   The value of nuh_layer_id of the VCL NAL unit is less than the    nuh_layer_id of the previous picture in decoding order.-   The value of ph_pic_order_cnt_lsb of the VCL NAL unit differs from    the ph_pic_order_cnt_lsb of the previous picture in decoding order.-   PicOrderCntVal derived for the VCL NAL unit differs from the    PicOrderCntVal of the previous picture in decoding order.

Let firstVclNalUnitInAu be the first VCL NAL unit of an AU. The first ofany of the following NAL units preceding firstVclNalUnitInAu andsucceeding the last VCL NAL unit preceding firstVclNalUnitInAu, if any,specifies the start of a new AU:

-   AUD NAL unit (when present),-   DCI NAL unit (when present),-   VPS NAL unit (when present),-   SPS NAL unit (when present),-   PPS NAL unit (when present),-   Prefix APS NAL unit (when present),-   PH NAL unit (when present),-   Prefix SEI NAL unit (when present),-   NAL unit with nal_unit_type equal to RSV_NVCL_26 (when present),-   NAL unit with nal_unit_type in the range of UNSPEC28..UNSPEC29 (when    present).

NOTE - The first NAL unit preceding firstVclNalUnitInAu and succeedingthe last VCL NAL unit preceding firstVclNalUnitInAu, if any, can only beone of the above-listed NAL units.

It is a requirement of bitstream conformance that, when present, thenext PU of a particular layer after a PU that belongs to the same layerand contains an EOS NAL unit shall be a CLVSS PU, which is either anIRAP PU with NoOutputBeforeRecoveryFlag equal to 1 or a GDR PU withNoOutputBeforeRecoveryFlag equal to 1.

4. Examples of Technical Problems Solved by Disclosed TechnicalSolutions

The existing scalability design in the latest VVC text (inJVET-Q2001-Ve/v15) has the following problems:

-   1) A CVSS AU, which starts a new CVS, is required to be complete    (i.e., to have a picture for each of the layers present in the CVS).    However, according to the current design, the decoder is not able to    check whether an AU includes a picture “for each of the layers    present in the CVS” before the decoder receives the last picture of    the CVS, while on the other hand, even the last picture of the CVS    is not easy to be determined because the last picture is not easy to    determine the start of any of CVS except for the very first CVS of    the bitstream. Basically, that means, the decoder can only figure    out the boundaries of CVSs after receiving the entire bitstream.-   2) Currently, an IRAP AU may start a new CVS and is required to be    complete (i.e., to have a picture for each of the layers present in    the CVS), while a GDR AU may also start a new CVS but is NOT    required to be complete. This basically disables random accessing a    bitstream starting from a GDR AU that is not complete in a    conforming manner, because usually the starting AU in random    accessing would become a CVSS AU but when such a GDR AU is    incomplete it cannot be a CVSS AU.

5. Example Embodiments and Techniques

To solve the above problems, and others, methods as summarized below aredisclosed. The embodiments should be considered as examples to explainthe general concepts and should not be interpreted in a narrow way.Furthermore, these embodiments can be applied individually or combinedin any manner. Solutions for solving the first problem

-   1) To solve the first problem, an indication of whether an AU is    complete, in the sense whether it includes a picture for each of the    layers present in the CVS, may be signaled.    -   a. In one example, the indication is signaled only for AUs that        may start a new CVS.        -   i. In one example, furthermore, the indication is signaled            only for AUs for which each picture is an IRAP or GDR            picture.    -   b. In one example, the indication is signaled in the AUD NAL        unit.        -   i. In one example, the indication is signaled by a flag            (e.g., irap_or_gdr_au_flag) in the AUD NAL unit.            -   1. Alternatively, additionally, when irap_or_gdr_au_flag                is equal to 1, a flag (i.e., named irap_au_flag) may be                signaled in the AUD to specify whether the AU is an IRAP                AU or a GDR AU (irap_au_flag equal to 1 specifies that                the AU is an IRAP AU, and irap_au_flag equal to 0                specifies that the AU is a GDR AU). No value of                irap_au_flag is inferred when it is not present.        -   ii. In one example, furthermore, one and only one AUD NAL            unit is required to be present in each IRAP or GDR AU when            vps_max_layers_minus1 is greater than 0.            -   1. Alternatively, one and only one AUD NAL unit is                required to be present in each IRAP or GDR AU regardless                of the value of vps_max_layers_minus1.        -   iii. In one example, the flag equal to 1 specifies that all            slices in the AU have the same NAL unit type in the range of            IDR_W_RADL to GDR_NUT, inclusive. Consequently, if the NAL            unit type is IDR_W_RADL or IDR_N_LP and this flag is equal            to 1, the AU is a CVSS AU. Otherwise (the NAL unit type is            CRA_NUT or GDR NUT), the AU is a CVSS AU when the variable            NoOutputBeforeRecoveryFlag for each of the pictures in the            AU is equal to 1.    -   c. In one example, furthermore, it is required that each picture        in an AU in a CVS shall have nuh _layer_id equal to the nuh        _layer_id of one of the pictures present in the first AU of the        CVS.    -   d. In one example, the indication is signaled in the NAL unit        header.        -   i. In one example, use a bit in the NAL unit header, e.g.,            nuh_reserved_zero_bit, to specify whether the AU is            complete.    -   e. In one example, the indication is signaled in a new NAL unit.        -   i. In one example, furthermore, the presence of one and only            one of the new NAL unit in each IRAP or GDR AU is required            when vps_max_layers_minus1 is greater than 0.            -   1. In one example, furthermore, when present in an AU,                the new NAL unit shall precede any NAL unit other than                the AUD NAL unit, when present, in the AU in decoding                order.            -   2. Alternatively, the presence of one and only one of                the new NAL unit in each IRAP or GDR AU is required                regardless of the value of vps_max_layers_minus1.    -   f. In one example, the indication is signaled in an SEI message.        -   i. In one example, furthermore, the presence of the SEI            message in each IRAP or GDR AU is required when vps_max            layers_minus1 is greater than 0.            -   1. In one example, furthermore, when present in an AU,                the SEI NAL unit containing the SEI message shall                precede any NAL unit other than the AUD NAL unit, when                present, in the AU in decoding order.            -   2. Alternatively, the presence of the SEI message in                each IRAP or GDR AU is required regardless of the value                of vps_max_layers_minus1.-   2) Alternatively, to solve the first problem, an indication of    whether an AU starts a new CVS may be signaled.    -   a. In one example, the indication is signaled in the AUD NAL        unit.        -   i. In one example, the indication is signaled by a flag            (e.g., irap_or_gdr_au_flag) in the AUD NAL unit.            -   1. Alternatively, additionally, when irap_or_gdr_au_flag                is equal to 1, a flag (i.e., named irap_au_flag) may be                signaled in the AUD to specify whether the AU is an IRAP                AU or a GDR AU (irap_au_flag equal to 1 specifies that                the AU is an IRAP AU, and irap_au_flag equal to 0                specifies that the AU is a GDR AU). No value of                irap_au_flag is inferred when it is not present.        -   ii. In one example, furthermore, one and only one AUD NAL            unit is required to be present in each CVSS AU when vps_max            layers_minus1 is greater than 0.            -   1. Alternatively, one and only one AUD NAL unit is                required to be present in each CVSS AU regardless of the                value of vps_max_layers_minus1.    -   b. In one example, the indication is signaled in the NAL unit        header.        -   i. In one example, use a bit in the NAL unit header, e.g.,            nuh_reserved_zero_bit, to specify whether the AU is a CVSS            AU.    -   c. In one example, the indication is signaled in a new NAL unit.        -   i. In one example, furthermore, the presence of one and only            one of the new NAL unit in each CVSS AU is required when            vps_max layers_minus1 is greater than 0.            -   1. In one example, furthermore, when present in an AU,                the new NAL unit shall precede any NAL unit other than                the AUD NAL unit, when present, in the AU in decoding                order.            -   2. Alternatively, the presence of one and only one of                the new NAL unit in each CVSS AU is required regardless                of the value of vps_max_layers_minus1.        -   ii. In one example, the presence of the new NAL unit in an            AU specifies that the AU is a CVSS AU.            -   1. Alternatively, a flag is included in the new NAL unit                to specify whether the AU is a CVSS AU.    -   d. In one example, the indication is signaled in an SEI message.        -   i. In one example, furthermore, the presence of the SEI            message in each CVSS AU is required when vps_max            layers_minus1 is greater than 0.            -   1. In one example, furthermore, when present in an AU,                the SEI NAL unit containing the SEI message shall                precede any NAL unit other than the AUD NAL unit, when                present, in the AU in decoding order.            -   2. Alternatively, the presence of the SEI message in                each CVSS AU is required regardless of the value of                vps_max_layers_minus1.-   3) Alternatively, to solve the first problem, a CVSS AU, which    starts a new CVS, is required to have a picture for each of the    layers specified by the VPS. Note that a shortcoming of this    approach is that then the number of layers signaled in the VPS needs    to be precise, and consequently when a layer is removed from the    bitstream the VPS needs to be modified.-   4) Alternatively, to solve the first problem, when vps_max    layers_minus1 is greater than 0, mandate the presence of the EOS NAL    unit for each picture in the last AU of each CVS, and optionally    also the presence of the EOB NAL unit in the last AU of each    bitstream. Thus each CVSS AU would be identified by either being the    first AU in the bitstream or the presence of the EOS NAL units in    the previous AU.-   5) Alternatively, to solve the first problem, an    external-means-determined variable is specified to specify whether    an AU is a CVSS AU.

Solutions for Solving the Second Problem

-   6) To solve the second problem, it is required that each GDR AU is    required to be complete (i.e., to have a picture for each of the    layers present in the CVS). That means, an AU consisting of GDR    pictures but if it is incomplete then it is not a GDR AU, similarly    as currently that an AU consisting of IRAP pictures but if it is    incomplete then it is not an IRAP AU.    -   a. In one example, a GDR AU may be defined as an AU in which        there is a PU for each layer in the CVS and the coded picture in        each present PU is a GDR picture.

6. Embodiments

Below are some example embodiments for some of the disclosed aspectssummarized above in Section 5, which can be applied to the VVCspecification. The changed texts are based on the latest VVC text inJVET-Q2001-Ve/v15. Most relevant parts that have been added or modifiedare shown in underline, bolded and italicized text, and the mostrelevant removed parts are highlighted in enclosed in bolded doublebrackets, e.g., indicates that “a” has been removed.. There are someother changes that are editorial in nature and thus not highlighted.

6.1. First Embodiment

This embodiment is for items 1, 1.a, 1.a.i, 1.b, 1.b.i, 1.b.ii, 1.b.iii,1.c, 6, and 6a.

3 Definitions

gradual decoding refresh (GDR) AU: An AU in which there is a PU for eachlayer in the CVS and the coded picture in each present PU is a GDRpicture.

7.3.2.9 AU delimiter RBSP syntax access_unit_delimiter_rbsp() {Descriptor  irap_or_gdr_au_flag u(1)  pic_type u(3) rbsp_trailing_bits() }

7.4.3.9 AU Delimiter RBSP Semantics

The AU delimiter is used to indicate the start of an AU, whether the A Uis an IRAP or GDR AU, and the type of slices present in the codedpictures in the AU containing the AU delimiter NAL unit. Forsingle-layer bitstreams, there is no normative decoding processassociated with the AU delimiter.

Irap or gdr_au_flag equal to 1 specifies that the AU containing the AUdelimiter is an IRAP or GDR AU. Irap_or_gdr_au_flag equal to 0 specifiesthat the AU containing the AU delimiter is not an IRAP or GDRAU.

7.4.2.4.2 Order of AUs and Their Association to CVSs

A bitstream consists of one or more CVSs.

A CVS consists of one or more AUs. The order of PUs and theirassociation to AUs are described in clause 7.4.2.4.3.

The first AU of a CVS is a CVSS AU, wherein each present PU is a CLVSSPU, which is either an IRAP PU with NoOutputBeforeRecoveryFlag equal to1 or a GDR PU with NoOutputBeforeRecoveryFlag equal to 1.

Each CVSS AU shall have a PU for each of the layers present in the CVSand each picture in an AU in a CVS shall have nuh_layer id equal to thenuh_layer id of one of the pictures present in the first AU of the CVS.

7.4.2.4.3 Order of PUs and Their Association to AUs

An AU consists of one or more PUs in increasing order of nuh_layer_id.The order NAL units and coded pictures and their association to PUs aredescribed in clause 7.4.2.4.4.

There can be at most one AUD NAL unit in an AU, and when vps max layersminus1 is greater than 0, there shall be one and only one AUD NAL unitin each IRAP or GDR AU.

When an AUD NAL unit is present in an AU, it shall be the first NAL unitof the AU, and consequently, it is the first NAL unit of the first PU ofthe AU.

There can be at most one EOB NAL unit in an AU. When an EOB NAL unit ispresent in an AU, it shall be the last NAL unit of the AU, andconsequently, it is the last NAL unit of the last PU of the AU.

FIG. 1 is a block diagram showing an example video processing system1000 in which various techniques disclosed herein may be implemented.Various implementations may include some or all of the components of thesystem 1000. The system 1000 may include input 1002 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 1002 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as wirelessfidelity (Wi-Fi) or cellular interfaces.

The system 1000 may include a coding component 1004 that may implementthe various coding or encoding methods described in the presentdocument. The coding component 1004 may reduce the average bitrate ofvideo from the input 1002 to the output of the coding component 1004 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 1004 may be eitherstored, or transmitted via a communication connected, as represented bythe component 1006. The stored or communicated bitstream (or coded)representation of the video received at the input 1002 may be used bythe component 1008 for generating pixel values or displayable video thatis sent to a display interface 1010. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include serial advanced technology attachment (SATA),peripheral component interconnect (PCI), integrated drive electronics(IDE) interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

FIG. 2 is a block diagram of a video processing apparatus 2000. Theapparatus 2000 may be used to implement one or more of the methodsdescribed herein. The apparatus 2000 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 2000 may include one or more processors 2002, one or morememories 2004 and video processing hardware 2006. The processor(s) 2002may be configured to implement one or more methods described in thepresent document. The memory (memories) 2004 may be used for storingdata and code used for implementing the methods and techniques describedherein. The video processing hardware 2006 may be used to implement, inhardware circuitry, some techniques described in the present document.In some embodiments, the hardware 2006 may be partly or entirely in theone or more processors 2002, e.g., a graphics processor.

FIG. 3 is a block diagram that illustrates an example video codingsystem 100 that may utilize the techniques of this disclosure.

As shown in FIG. 3 , video coding system 100 may include a source device110 and a destination device 120. Source device 110 generates encodedvideo data which may be referred to as a video encoding device.Destination device 120 may decode the encoded video data generated bysource device 110 which may be referred to as a video decoding device.

Source device 110 may include a video source 112, a video encoder 114,and an input/output (I/O) interface 116.

Video source 112 may include a source such as a video capture device, aninterface to receive video data from a video content provider, and/or acomputer graphics system for generating video data, or a combination ofsuch sources. The video data may comprise one or more pictures. Videoencoder 114 encodes the video data from video source 112 to generate abitstream. The bitstream may include a sequence of bits that form acoded representation of the video data. The bitstream may include codedpictures and associated data. The coded picture is a codedrepresentation of a picture. The associated data may include sequenceparameter sets, picture parameter sets, and other syntax structures. I/Ointerface 116 may include a modulator/demodulator (modem) and/or atransmitter. The encoded video data may be transmitted directly todestination device 120 via I/O interface 116 through network 130 a. Theencoded video data may also be stored onto a storage medium/server 130 bfor access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface126 may acquire encoded video data from the source device 110 or thestorage medium/ server 130 b. Video decoder 124 may decode the encodedvideo data. Display device 122 may display the decoded video data to auser. Display device 122 may be integrated with the destination device120, or may be external to destination device 120 which be configured tointerface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard, Versatile Video Coding (VVC) standard and other current and/orfurther standards.

FIG. 4 is a block diagram illustrating an example of video encoder 200,which may be video encoder 114 in the system 100 illustrated in FIG. 3 .

Video encoder 200 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 4 , video encoder200 includes a plurality of functional components. The techniquesdescribed in this disclosure may be shared among the various componentsof video encoder 200. In some examples, a processor may be configured toperform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partitionunit 201, a prediction unit 202 which may include a mode select unit203, a motion estimation unit 204, a motion compensation unit 205 and anintra prediction unit 206, a residual generation unit 207, a transformunit 208, a quantization unit 209, an inverse quantization unit 210, aninverse transform unit 211, a reconstruction unit 212, a buffer 213, andan entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, ordifferent functional components. In an example, prediction unit 202 mayinclude an intra block copy (IBC) unit. The IBC unit may performprediction in an IBC mode in which at least one reference picture is apicture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 andmotion compensation unit 205 may be highly integrated, but arerepresented in the example of FIG. 4 separately for purposes ofexplanation.

Partition unit 201 may partition a picture into one or more videoblocks. Video encoder 200 and video decoder 300 may support variousvideo block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter,e.g., based on error results, and provide the resulting intra- orinter-coded block to a residual generation unit 207 to generate residualblock data and to a reconstruction unit 212 to reconstruct the encodedblock for use as a reference picture. In some example, mode select unit203 may select a combination of intra and inter prediction (CIIP) modein which the prediction is based on an inter prediction signal and anintra prediction signal. Mode select unit 203 may also select aresolution for a motion vector (e.g., a sub-pixel or integer pixelprecision) for the block in the case of inter-prediction.

To perform inter prediction on a current video block, motion estimationunit 204 may generate motion information for the current video block bycomparing one or more reference frames from buffer 213 to the currentvideo block. Motion compensation unit 205 may determine a predictedvideo block for the current video block based on the motion informationand decoded samples of pictures from buffer 213 other than the pictureassociated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may performdifferent operations for a current video block, for example, dependingon whether the current video block is in an I slice, a P slice, or a Bslice.

In some examples, motion estimation unit 204 may perform uni-directionalprediction for the current video block, and motion estimation unit 204may search reference pictures of list 0 or list 1 for a reference videoblock for the current video block. Motion estimation unit 204 may thengenerate a reference index that indicates the reference picture in list0 or list 1 that contains the reference video block and a motion vectorthat indicates a spatial displacement between the current video blockand the reference video block. Motion estimation unit 204 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the current video block. Motioncompensation unit 205 may generate the predicted video block of thecurrent block based on the reference video block indicated by the motioninformation of the current video block.

In other examples, motion estimation unit 204 may perform bi-directionalprediction for the current video block, motion estimation unit 204 maysearch the reference pictures in list 0 for a reference video block forthe current video block and may also search the reference pictures inlist 1 for another reference video block for the current video block.Motion estimation unit 204 may then generate reference indexes thatindicate the reference pictures in list 0 and list 1 containing thereference video blocks and motion vectors that indicate spatialdisplacements between the reference video blocks and the current videoblock. Motion estimation unit 204 may output the reference indexes andthe motion vectors of the current video block as the motion informationof the current video block. Motion compensation unit 205 may generatethe predicted video block of the current video block based on thereference video blocks indicated by the motion information of thecurrent video block.

In some examples, motion estimation unit 204 may output a full set ofmotion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may not output a full setof motion information for the current video. Rather, motion estimationunit 204 may signal the motion information of the current video blockwith reference to the motion information of another video block. Forexample, motion estimation unit 204 may determine that the motioninformation of the current video block is sufficiently similar to themotion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntaxstructure associated with the current video block, a value thatindicates to the video decoder 300 that the current video block has thesame motion information as another video block.

In another example, motion estimation unit 204 may identify, in a syntaxstructure associated with the current video block, another video blockand a motion vector difference (MVD). The motion vector differenceindicates a difference between the motion vector of the current videoblock and the motion vector of the indicated video block. The videodecoder 300 may use the motion vector of the indicated video block andthe motion vector difference to determine the motion vector of thecurrent video block.

As discussed above, video encoder 200 may predictively signal the motionvector. Two examples of predictive signaling techniques that may beimplemented by video encoder 200 include advanced motion vectorprediction (AMVP) and merge mode signaling.

Intra prediction unit 206 may perform intra prediction on the currentvideo block. When intra prediction unit 206 performs intra prediction onthe current video block, intra prediction unit 206 may generateprediction data for the current video block based on decoded samples ofother video blocks in the same picture. The prediction data for thecurrent video block may include a predicted video block and varioussyntax elements.

Residual generation unit 207 may generate residual data for the currentvideo block by subtracting (e.g., indicated by the minus sign) thepredicted video block(s) of the current video block from the currentvideo block. The residual data of the current video block may includeresidual video blocks that correspond to different sample components ofthe samples in the current video block.

In other examples, there may be no residual data for the current videoblock for the current video block, for example in a skip mode, andresidual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transformcoefficient video blocks for the current video block by applying one ormore transforms to a residual video block associated with the currentvideo block.

After transform processing unit 208 generates a transform coefficientvideo block associated with the current video block, quantization unit209 may quantize the transform coefficient video block associated withthe current video block based on one or more quantization parameter (QP)values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may applyinverse quantization and inverse transforms to the transform coefficientvideo block, respectively, to reconstruct a residual video block fromthe transform coefficient video block. Reconstruction unit 212 may addthe reconstructed residual video block to corresponding samples from oneor more predicted video blocks generated by the prediction unit 202 toproduce a reconstructed video block associated with the current blockfor storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loopfiltering operation may be performed reduce video blocking artifacts inthe video block.

Entropy encoding unit 214 may receive data from other functionalcomponents of the video encoder 200. When entropy encoding unit 214receives the data, entropy encoding unit 214 may perform one or moreentropy encoding operations to generate entropy encoded data and outputa bitstream that includes the entropy encoded data.

FIG. 5 is a block diagram illustrating an example of video decoder 300which may be video decoder 124 in the system 100 illustrated in FIG. 3 .

The video decoder 300 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 5 , the videodecoder 300 includes a plurality of functional components. Thetechniques described in this disclosure may be shared among the variouscomponents of the video decoder 300. In some examples, a processor maybe configured to perform any or all of the techniques described in thisdisclosure.

In the example of FIG. 5 , video decoder 300 includes an entropydecoding unit 301, a motion compensation unit 302, an intra predictionunit 303, an inverse quantization unit 304, an inverse transformationunit 305, and a reconstruction unit 306 and a buffer 307. Video decoder300 may, in some examples, perform a decoding pass generally reciprocalto the encoding pass described with respect to video encoder 200 (FIG. 4).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encodedbitstream may include entropy coded video data (e.g., encoded blocks ofvideo data). Entropy decoding unit 301 may decode the entropy codedvideo data, and from the entropy decoded video data, motion compensationunit 302 may determine motion information including motion vectors,motion vector precision, reference picture list indexes, and othermotion information. Motion compensation unit 302 may, for example,determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks,possibly performing interpolation based on interpolation filters.Identifiers for interpolation filters to be used with sub-pixelprecision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used byvideo encoder 200 during encoding of the video block to calculateinterpolated values for sub-integer pixels of a reference block. Motioncompensation unit 302 may determine the interpolation filters used byvideo encoder 200 according to received syntax information and use theinterpolation filters to produce predictive blocks.

Motion compensation unit 302 may use some of the syntax information todetermine sizes of blocks used to encode frame(s) and/or slice(s) of theencoded video sequence, partition information that describes how eachmacroblock of a picture of the encoded video sequence is partitioned,modes indicating how each partition is encoded, one or more referenceframes (and reference frame lists) for each inter-encoded block, andother information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for examplereceived in the bitstream to form a prediction block from spatiallyadjacent blocks. Inverse quantization unit 303 inverse quantizes, i.e.,de-quantizes, the quantized video block coefficients provided in thebitstream and decoded by entropy decoding unit 301. Inverse transformunit 303 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with thecorresponding prediction blocks generated by motion compensation unit302 or intra-prediction unit 303 to form decoded blocks. If desired, adeblocking filter may also be applied to filter the decoded blocks inorder to remove blockiness artifacts. The decoded video blocks are thenstored in buffer 307, which provides reference blocks for subsequentmotion compensation/intra prediction and also produces decoded video forpresentation on a display device.

FIGS. 6-7 show example methods that can implement the technical solutiondescribed above in, for example, the embodiments shows in FIGS. 1-5 .

FIG. 6 shows a flowchart for an example method 600 of video processing.The method 600 includes, at operation 610, performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of a video, the bitstream comprising a codedvideo sequence (CVS) that includes one or more access units (AUs), andthe bitstream further comprising a first syntax element indicatingwhether an AU includes a picture for each video layer making up the CVS.

FIG. 7 shows a flowchart for an example method 700 of video processing.The method 700 includes, at operation 710, performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of the video, the bitstream comprising a codedvideo sequence (CVS) that includes one or more access units (AUs), andthe bitstream conforming to a format rule that specifies that eachpicture in a given AU carries a layer identifier that is equal to alayer identifier of a first AU of the CVS comprising the one or morevideo layers.

FIG. 8 shows a flowchart for an example method 800 of video processing.The method 800 includes, at operation 810, performing, a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of a video, the bitstream comprising a codedvideo sequence (CVS) that includes one or more access units (AUs), andthe bitstream further comprising a first syntax element indicative of anAU of the one or more AUs starting a new CVS.

FIG. 9 shows a flowchart for an example method 900 of video processing.The method 900 includes, at operation 910, performing a conversionbetween a video comprising one or more pictures in one or more videolayers and a bitstream of the video, the bitstream comprising a codedvideo sequence (CVS) that includes one or more access units (AUs), andthe bitstream conforming to a format rule that specifies that a codedvideo sequence start (CVSS) AU, which starts a new CVS, comprises apicture for each video layer specified in a video parameter set (VPS).

FIG. 10 shows a flowchart for an example method 1000 of videoprocessing. The method 1000 includes, at operation 1010, performing aconversion between a video comprising one or more pictures in one ormore video layers and a bitstream of the video, the bitstream comprisinga coded video sequence (CVS) that includes one or more access units(AUs), and the bitstream conforming to a format rule that specifies thata given AU is identified as a coded video sequence start (CVSS) AU basedon the given AU being a first AU in the bitstream or an AU previous tothe given AU comprising end of sequence (EOS) network abstraction layer(NAL) units.

FIG. 11 shows a flowchart for an example method 1100 of videoprocessing. The method 1100 includes, at operation 1110, performing,based on a rule, a conversion between a video comprising one or morepictures in one or more video layers and a bitstream of the video, thebitstream comprising a coded video sequence (CVS) that includes one ormore access units (AUs), and the rule specifying that side informationis used to indicate whether an AU of the one or more AUs is a codedvideo sequence start (CVSS) AU.

FIG. 12 shows a flowchart for an example method 1200 of videoprocessing. The method 1200 includes, at operation 1210, performing aconversion between a video comprising one or more pictures in one ormore video layers and a bitstream of a video, the bitstream comprising acoded video sequence (CVS) that includes one or more access units (AUs),and the bitstream conforming to a format rule that specifies that eachAU of the one or more AUs that is a gradual decoding refresh AU includesexactly one picture for each video layer present in the CVS.

FIG. 13 shows a flowchart for an example method 1300 of videoprocessing. The method 1300 includes, at operation 1310, performing aconversion between a video comprising one or more pictures in one ormore video layers and a bitstream of a video, the bitstream comprising acoded video sequence that includes one or more access units (AUs), andthe bitstream conforming to a format rule that specifies that each AU ofthe one or more AUs that is an intra random access points AU includesexactly one picture for each video layer present in the CVS.

A listing of solutions preferred by some embodiments is provided next.

-   P1. A video processing method, comprising performing a conversion    between a video having one or more pictures in one or more video    layers and a coded representation representing an encoded version of    the video; wherein the coded representation includes one or more    access units (AU); wherein the coded representation includes a    syntax element if and only if an AU is of a type, wherein the syntax    element indicates whether the AU includes a picture for each video    layer making up a coded video sequence.-   P2. The method of solution P1, wherein the type includes all AUs.-   P3. The method of solution P1, wherein the type includes AUs that    start a new CVS.-   P4. The method of solution P1, wherein the syntax element is    included in an access unit delimiter network abstraction layer unit.-   P5. The method of any of solutions P1 to P4, wherein the syntax    element is included in a network abstraction layer unit header.-   P6. The method of any of solutions P 1 to P4, wherein the syntax    element is included in new a network abstraction layer unit.-   P7. A video processing method, comprising performing a conversion    between a video having one or more pictures in one or more video    layers and a coded representation representing an encoded version of    the video; wherein the coded representation includes one or more    access units (AU); wherein the coded representation conforms to a    format rule that specifies that each picture in a given AU carries a    layer identifier that is equal to that of a first AU of a coded    video sequence.-   P8. A video processing method, comprising performing a conversion    between a video having one or more pictures in one or more video    layers and a coded representation representing an encoded version of    the video; wherein the coded representation includes one or more    access units (AU); wherein the coded representation includes a    syntax element if and only if an AU starts a new coded video    sequence.-   P9. The method of solution P8, wherein the syntax element is    included in an access unit delimiter network abstraction layer unit.-   P10. The method of any of solutions P8 to P9, wherein the syntax    element is included in a network abstraction layer unit header.-   P11. The method of any of solutions P8 to P9, wherein the syntax    element is included as a supplemental enhancement information.-   P12. A video processing method, comprising performing a conversion    between a video having one or more pictures in one or more video    layers and a coded representation of the video; wherein the coded    representation includes one or more access units (AU); wherein the    coded representation conforms to a format rule that specifies that a    starting AU for a coded video sequence includes a video picture for    each video layer specified by a video parameter set or that the    coded representation implicitly signals the starting AU based on a    rule.-   P13. A video processing method, comprising performing a conversion    between a video having one or more pictures in one or more video    layers and a coded representation of the video; wherein the coded    representation includes one or more access units (AU); wherein the    coded representation conforms to a format rule that specifies that    each AU of type gradual decoding refresh (GDR) includes at least a    video picture for each video layer of a coded video sequence.-   P14. The method of solution P13, wherein each AU of type GDR further    includes a prediction unit for each layer in the CVS and the PU    comprises GDR pictures.-   P15. The method of any of solutions P1 to 14, wherein the conversion    comprises encoding the video into the coded representation.-   P16. The method of any of solutions P1 to 14, wherein the conversion    comprises decoding the coded representation to generate pixel values    of the video.-   P17. A video decoding apparatus comprising a processor configured to    implement a method recited in one or more of solutions P1 to P16.-   P18. A video encoding apparatus comprising a processor configured to    implement a method recited in one or more of solutions P1 to P16.    P19. A computer program product having computer code stored thereon,    the code, when executed by a processor, causes the processor to    implement a method recited in any of solutions P1 to P16.

Another listing of solutions preferred by some embodiments is providednext.

-   A1. A method of video processing, comprising performing a conversion    between a video comprising one or more pictures in one or more video    layers and a bitstream of a video, wherein the bitstream comprises a    coded video sequence that includes one or more access units, and    wherein the bitstream further comprises a first syntax element    indicating whether an access unit includes a picture for each video    layer making up the coded video sequence.-   A2. The method of solution A1, wherein the access unit is configured    to start a new coded video sequence.-   A3. The method of solution A2, wherein the picture for each video    layer is an intra random access point picture or a gradual decoding    refresh picture.-   A4. The method of solution A1, wherein the first syntax element is    included in an access unit delimiter network abstraction layer unit.-   A5. The method of solution A4, wherein the first syntax element is a    flag indicating whether an access unit containing an access unit    delimiter is an intra random access point access unit or a gradual    decoding refresh access unit.-   A6. The method of solution A5, wherein the first syntax element is    irap_or_gdr_au_flag.-   A7. The method of solution A4, wherein the access unit delimiter    network abstraction layer unit is the only access unit delimiter    network abstraction layer unit present in each intra random access    point access unit or gradual decoding refresh access unit when a    second syntax element, which is indicative of a number of video    layers specified by a video parameter set, is greater than one.-   A8. The method of solution A7, wherein the second syntax element    indicates a maximum allowed number of layers in each coded video    sequence that refers to the video parameter set.-   A9. The method of solution A1, wherein the first syntax element    equaling one is indicative of all slices in the access unit    comprising an identical network abstraction layer unit type in a    range of IDR_W_RADL to GDR_NUT, inclusive.-   A10. The method of solution A9, wherein the first syntax element    equaling one and the network abstraction layer unit type being    IDR_W_RADL or IDR_N_LP is indicative of the access unit being a    coded video sequence start access unit.-   A11. The method of solution A9, wherein a variable for each of the    pictures in the access unit equaling one and the network abstraction    layer unit type being CRA_NUT or GDR_NUT is indicative of the access    unit being a coded video sequence start access unit.-   A12. The method of solution A11, wherein the variable indicates    whether pictures in a decoded picture buffer prior to a current    picture in decoding order are output before the pictures are    recovered.-   A13. The method of solution A11, wherein the variable is    NoOutputBeforeRecoveryFlag.-   A14. The method of solution A1, wherein the first syntax element is    included in a network abstraction layer unit header.-   A15. The method of solution A1, wherein the first syntax element is    included in a new network abstraction layer unit.-   A16. The method of solution A15, wherein the new network abstraction    layer unit is the only new network abstraction layer unit present in    each intra random access point access unit or gradual decoding    refresh access unit when a second syntax element, which is    indicative of a number of video layers specified by a video    parameter set, is greater than one.-   A17. The method of solution A1, wherein the first syntax element is    included in a supplementary enhancement information message.-   A18. The method of solution A17, wherein the supplementary    enhancement information message is the only supplementary    enhancement information message present in each intra random access    point access unit or gradual decoding refresh access unit when a    second syntax element, which is indicative of a number of video    layers specified by a video parameter set, is greater than zero.-   A19. A method of video processing, comprising performing a    conversion between a video comprising one or more pictures in one or    more video layers and a bitstream of the video, wherein the    bitstream comprises a coded video sequence that includes one or more    access units, and wherein the bitstream conforms to a format rule    that specifies that each picture in a given access unit carries a    layer identifier that is equal to a layer identifier of a first    access unit of the coded video sequence comprising the one or more    video layers.-   A20. A method of video processing, comprising performing, a    conversion between a video comprising one or more pictures in one or    more video layers and a bitstream of a video, wherein the bitstream    comprises a coded video sequence that includes one or more access    units, and wherein the bitstream further comprises a first syntax    element indicative of an access unit of the one or more access units    starting a new coded video sequence.-   A21. The method of solution A20, wherein the first syntax element is    included in an access unit delimiter network abstraction layer unit.-   A22. The method of solution A20, wherein the first syntax element is    included in a network abstraction layer unit header.-   A23. The method of solution A20, wherein the first syntax element is    included in a new network abstraction layer unit.-   A24. The method of solution A20, wherein the first syntax element is    included in a supplementary enhancement information message.-   A25. A method of video processing, comprising performing a    conversion between a video comprising one or more pictures in one or    more video layers and a bitstream of the video, wherein the    bitstream comprises a coded video sequence that includes one or more    access units, and wherein the bitstream conforms to a format rule    that specifies that a coded video sequence start access unit, which    starts a new coded video sequence, comprises a picture for each    video layer specified in a video parameter set.-   A26. A method of video processing, comprising performing a    conversion between a video comprising one or more pictures in one or    more video layers and a bitstream of the video, wherein the    bitstream comprises a coded video sequence that includes one or more    access units, and wherein the bitstream conforms to a format rule    that specifies that a given access unit is identified as a coded    video sequence start access unit based on the given access unit    being a first access unit in the bitstream or an access unit    previous to the given access unit comprising end of sequence network    abstraction layer units.-   A27. A method of video processing, comprising performing, based on a    rule, a conversion between a video comprising one or more pictures    in one or more video layers and a bitstream of the video, wherein    the bitstream comprises a coded video sequence that includes one or    more access units, and wherein the rule specifies that side    information is used to indicate whether an access unit of the one or    more access units is a coded video sequence start access unit.-   A28. The method of any of solutions A1 to A27, wherein the    conversion comprises decoding the video from the bitstream.-   A29. The method of any of solutions A1 to A27, wherein the    conversion comprises encoding the video into the bitstream.-   A30. A method of storing a bitstream representing a video to a    computer-readable recording medium, comprising generating the    bitstream from the video according to a method described in any one    or more of solutions A1 to A27; and storing the bitstream in the    computer-readable recording medium.-   A31. A video processing apparatus comprising a processor configured    to implement a method recited in any one or more of solutions A1 to    A30.-   A32. A computer-readable medium having instructions stored thereon,    the instructions, when executed, causing a processor to implement a    method recited in one or more of solutions A1 to A30.-   A33. A computer readable medium that stores the bitstream generated    according to any one or more of solutions A1 to A30.-   A34. A video processing apparatus for storing a bitstream, wherein    the video processing apparatus is configured to implement a method    recited in any one or more of solutions A1 to A30.

Yet another listing of solutions preferred by some embodiments isprovided next.

-   B1. A method of video processing, comprising performing a conversion    between a video comprising one or more pictures in one or more video    layers and a bitstream of a video, wherein the bitstream comprises a    coded video sequence that includes one or more access units, and    wherein the bitstream conforms to a format rule that specifies that    each access unit of the one or more access units that is a gradual    decoding refresh access unit includes exactly one picture for each    video layer present in the coded video sequence.-   B2. The method of solution B1, wherein each access unit that is a    gradual decoding refresh access unit includes a prediction unit for    each layer present in the coded video sequence, and wherein the    prediction unit for each layer includes a coded picture that is a    gradual decoding refresh picture.-   B3. A method of video processing, comprising performing a conversion    between a video comprising one or more pictures in one or more video    layers and a bitstream of a video, wherein the bitstream comprises a    coded video sequence that includes one or more access units, and    wherein the bitstream conforms to a format rule that specifies that    each access unit of the one or more access units that is an intra    random access points access unit includes exactly one picture for    each video layer present in the coded video sequence.-   B4. The method of any of solutions B1 to B3, wherein the conversion    comprises decoding the video from the bitstream.-   B5. The method of any of solutions B1 to B3, wherein the conversion    comprises encoding the video into the bitstream.-   B6. A method of storing a bitstream representing a video to a    computer-readable recording medium, comprising generating the    bitstream from the video according to a method described in any one    or more of solutions B1 to B3; and storing the bitstream in the    computer-readable recording medium.-   B7. A video processing apparatus comprising a processor configured    to implement a method recited in any one or more of solutions B1 to    B6.-   B8. A computer-readable medium having instructions stored thereon,    the instructions, when executed, causing a processor to implement a    method recited in one or more of solutions B 1 to B6.-   B9. A computer readable medium that stores the bitstream generated    according to any one or more of solutions B1 to B6.-   B10. A video processing apparatus for storing a bitstream, wherein    the video processing apparatus is configured to implement a method    recited in any one or more of solutions B1 to B6.

In the present document, the term “video processing” may refer to videoencoding, video decoding, video compression or video decompression. Forexample, video compression algorithms may be applied during conversionfrom pixel representation of a video to a corresponding bitstreamrepresentation or vice versa. The bitstream representation of a currentvideo block may, for example, correspond to bits that are eitherco-located or spread in different places within the bitstream, as isdefined by the syntax. For example, a macroblock may be encoded in termsof transformed and coded error residual values and also using bits inheaders and other fields in the bitstream. Furthermore, duringconversion, a decoder may parse a bitstream with the knowledge that somefields may be present, or absent, based on the determination, as isdescribed in the above solutions. Similarly, an encoder may determinethat certain syntax fields are or are not to be included and generatethe coded representation accordingly by including or excluding thesyntax fields from the coded representation.

The disclosed and other solutions, examples, embodiments, modules andthe functional operations described in this document can be implementedin digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this document and theirstructural equivalents, or in combinations of one or more of them. Thedisclosed and other embodiments can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a computer readable medium for execution by, orto control the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them. A propagated signal is anartificially generated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal, that is generated to encodeinformation for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., a field programmable gate array (FPGA) or anapplication specific integrated circuit (ASIC).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., erasable programmable read-onlymemory (EPROM), electrically erasable programmable read-only memory(EEPROM), and flash memory devices; magnetic disks, e.g., internal harddisks or removable disks; magneto optical disks; and compact disc,read-only memory (CD ROM) and digital versatile disc read-only memory(DVD-ROM) disks. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any subject matter or of whatmay be claimed, but rather as descriptions of features that may bespecific to particular embodiments of particular techniques. Certainfeatures that are described in this patent document in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method of video processing, comprising:performing a conversion between a video comprising one or more picturesin one or more video layers and a bitstream of the video, wherein thebitstream comprises a coded video sequence that includes one or moreaccess units, and wherein the bitstream conforms to a first format rulethat specifies that each access unit of the one or more access unitsthat is a gradual decoding refresh access unit includes at least onepicture for each video layer present in the coded video sequence.
 2. Themethod of claim 1, wherein the gradual decoding refresh access unitincludes exactly one picture for each video layer present in the codedvideo sequence.
 3. The method of claim 1, wherein each access unit thatis the gradual decoding refresh access unit includes a prediction unitfor each layer present in the coded video sequence, and wherein theprediction unit for each layer includes a coded picture that is thegradual decoding refresh picture.
 4. The method of claim 1, wherein thebitstream conforms to a second format rule that specifies that eachaccess unit of the one or more access units that is an intra randomaccess points access unit includes exactly one picture for each videolayer present in the coded video sequence.
 5. The method of claim 1,wherein the conversion comprises decoding the video from the bitstream.6. The method of claim 1, wherein the conversion comprises encoding thevideo into the bitstream.
 7. An apparatus for processing video datacomprising a processor and a non-transitory memory with instructionsthereon, wherein the instructions upon execution by the processor, causethe processor to: perform a conversion between a video comprising one ormore pictures in one or more video layers and a bitstream of the video,wherein the bitstream comprises a coded video sequence that includes oneor more access units, and wherein the bitstream conforms to a firstformat rule that specifies that each access unit of the one or moreaccess units that is a gradual decoding refresh access unit includes atleast one picture for each video layer present in the coded videosequence.
 8. The apparatus of claim 7, wherein the gradual decodingrefresh access unit includes exactly one picture for each video layerpresent in the coded video sequence.
 9. The apparatus of claim 7,wherein each access unit that is the gradual decoding refresh accessunit includes a prediction unit for each layer present in the codedvideo sequence, and wherein the prediction unit for each layer includesa coded picture that is the gradual decoding refresh picture.
 10. Theapparatus of claim 7, wherein the bitstream conforms to a second formatrule that specifies that each access unit of the one or more accessunits that is an intra random access points access unit includes exactlyone picture for each video layer present in the coded video sequence.11. The apparatus of claim 7, wherein the conversion comprises decodingthe video from the bitstream.
 12. The apparatus of claim 7, wherein theconversion comprises encoding the video into the bitstream.
 13. Anon-transitory computer-readable storage medium storing instructionsthat cause a processor to: perform a conversion between a videocomprising one or more pictures in one or more video layers and abitstream of the video, wherein the bitstream comprises a coded videosequence that includes one or more access units, and wherein thebitstream conforms to a first format rule that specifies that eachaccess unit of the one or more access units that is a gradual decodingrefresh access unit includes at least one picture for each video layerpresent in the coded video sequence.
 14. The medium of claim 13, whereinthe gradual decoding refresh access unit includes exactly one picturefor each video layer present in the coded video sequence.
 15. The mediumof claim 13, wherein each access unit that is the gradual decodingrefresh access unit includes a prediction unit for each layer present inthe coded video sequence, and wherein the prediction unit for each layerincludes a coded picture that is the gradual decoding refresh picture.16. The medium of claim 13, wherein the bitstream conforms to a secondformat rule that specifies that each access unit of the one or moreaccess units that is an intra random access points access unit includesexactly one picture for each video layer present in the coded videosequence.
 17. A non-transitory computer-readable recording mediumstoring a bitstream of a video which is generated by a method performedby a video processing apparatus, wherein the method comprises:generating the bitstream of the video comprising one or more pictures inone or more video layers, wherein the bitstream comprises a coded videosequence that includes one or more access units, and wherein thebitstream conforms to a first format rule that specifies that eachaccess unit of the one or more access units that is a gradual decodingrefresh access unit includes at least one picture for each video layerpresent in the coded video sequence.
 18. The medium of claim 17, whereinthe gradual decoding refresh access unit includes exactly one picturefor each video layer present in the coded video sequence.
 19. The mediumof claim 17, wherein each access unit that is the gradual decodingrefresh access unit includes a prediction unit for each layer present inthe coded video sequence, and wherein the prediction unit for each layerincludes a coded picture that is the gradual decoding refresh picture.20. The medium of claim 17, wherein the bitstream conforms to a secondformat rule that specifies that each access unit of the one or moreaccess units that is an intra random access points access unit includesexactly one picture for each video layer present in the coded videosequence.